Additive color overlay
Final &amp; Overview:




  This is partial answer. It's solves question but not other possibilities.


You can Add or Mix Diffuse shader with Transparent shader. Diffuse should be color you want to have after mix and Transparent is a base color. Text has just Diffuse shader.

Why partial?

Well, it will work only with few colors (yellow + red = orange is working too). I don't know why, and I can't find a proper answer, but if you'll want to mix for example red with blue to get magenta it will fail. 

Another con of this method is that you'll need to know how colors are mixing and set it manually.

I hope that someone could elaborate about this issue more. It's pretty interesting.